Method of manufacturing rubber modified styrene resins

ABSTRACT

A method of manufacturing rubber modified styrene resins comprising the 1st step of polymerizing a styrene monomer in the presence of a butadiene polymer and an organic peroxide at the ratio of 100 parts by weight, 3 to 15 parts by weight and 0 to 0.01 parts by weight respectively until the polymerization yield of the styrene monomer becomes 2 to 5 time more than the weight of the butadiene polymer, and the 2nd step of polymerizing the full amount of polymer mixture from the 1st step and 0 to 200 parts by weight of the fresh styrene monomer in the presence of 0.01 to 0.9 parts by weight of the organic peroxide until the polymerization yield of the styrene monomer becomes at least 1.5 times more than that of the 1st step. The molded product of the resin thus obtained shows an improved impact strength at the portions wherein polystyrene molecule orientation tends to occur.

TECHNICAL FIELD

The present invention concerns a method of manufacturing rubber modifiedstyrene resins having an excellent impact resistance. More particularly,the present invention concerns a method of continuously manufacturingrubber modified styrene resins with a remarkably improved impactresistance at the portions where polystyrene molecule orientation tendsto occur in the molded product.

Background of Art

In the conventional art, rubber modified styrene resins are manufacturedby the continuous bulk polymerization or solution polymerization or bythe batch type bulk-suspension polymerization method. There have beenproposed various methods for continuously manufacturing rubber modifiedstyrene resin in the art. One of the methods which uses organic peroxideis disclosed in Japanese Patent Publication No. 37233/1976. As the usesfor rubber modified styrene resins are becoming more and morediversified and multiplied today, and the said resins are used as amaterial for complicatedly shaped molded products, an extremelyimportant problem facing the industry concerned is to secure the impactstrength at the portions where polystyrene molecule orientation tends tooccur within the molded product.

In other words, the rubber modified styrene resins obtained by theconventional manufacturing method have the problem in that when moldedinto a complex shape certain portions tend to become destroyed by theimpact caused by the crash of an object during actual use. When such aphenomenon of the destruction was studied, it was found that the portionin question coincided with the portion where orientation of thepolystyrene molecules tended to occur, and judging from the results bythe evaluation of falling weight impact test, the impact strength wherepolystyrene molecule orientation tended to occur in the molded productdecreased inordinately.

Generally such a degree of orientation in the styrene resin moldedproduct depends on the molding conditions, but it may also be improvedby the manufacturing method of the resin itself.

The object of the present invention is to provide a method formanufacturing rubber modified styrene resin with an improved impactstrength at the portions where polystyrene molecule orientation tends tooccur in the molded product.

DISCLOSURE OF THE INVENTION

"The portions where polystyrene molecule orientation tends to occur inthe molded product" as mentioned in the following discussion of thepresent invention coincide with the portions where excessive thermalcontraction occurs at the time of heating (80°-120° C.) when the productis molded with polystyrene resins. The absolute amount of thermalcontraction depends on the molding conditions, but it was found that theimpact strength at the portions with a relatively larger degree ofthermal contraction was uniquely lower in the molded product with acomplex shape.

Surprisingly, if the resin was manufactured by the continuouspolymerization method where organic peroxide, initiator for radicalpolymerization, was supplied under specifically restricted conditions,the impact strength was observed to improve greatly at the portionswhere polystyrene molecule orientation tended to occur in the moldedproduct. The present invention was completed based on this finding.

According to the present invention, there is provided a method ofmanufacturing rubber modified polystyrene resins:

In a method of manufacturing rubber modified styrene resins from astyrene monomer and a butadiene polymer by bulk polymerization orsolution polymerization method using an organic peroxide as aninitiator, the improvement which comprises

(A) the 1st step of polymerizing the styrene monomer in the presence ofbutadiene polymer and the organic peroxide at the ratio of 100 parts byweight, 3-15 parts by weight and 0-0.01 parts by weight respectivelyuntil the polymerization yield of the styrene monomer becomes 2 to 5times more than the weight of the butadiene polymer; and

(B) the 2nd step of polymerizing the full amount of polymerizationmixture of the 1st step and 0-200 parts by weight of the styrene monomerin the presence of 0.01-0.9 parts by weight of the organic peroxideuntil the polymerization yield of the styrene monomer becomes at least1.5 times more than that of the 1st step.

THE BEST MODE OF CARRYING OUT THE INVENTION

A preferred embodiment of the present invention for continuouslymanufacturing rubber modified styrene resins comprises the following: Ina method of continuously manufacturing rubber modified styrene resinsfrom a styrene monomer and a butadiene polymer by the solutionpolymerization or bulk polymerization method using an organic peroxideas an initiator for radical polymerization, the improvement comprisingthe steps of

(A) using single or plural number of agitator type polymerizationreactor connected in series, supplying 100 parts by weight of thestyrene monomer and 3-15 parts by weight of the butadiene polymer to the1st reactor which are to be supplied continuously per unit time, addingcontinuously the full amount of 0 to 0.01 parts by weight of organicperoxide to the 1st reactor or in divided portions to the plural numberof polymerization reactors, and conducting polymerization until thepolymerization yield to the styrene monomer becomes to the range of 2.0to 5.0 times more than the weight of the butadiene polymer in the finalreactor (hereinafter referred to as the step (A); and

(B) using a single or a plural number of reactors arranged in series,supplying continuously to the reactor in the 1st stage

(a) the full amount of polymerization liquid discharged from the step(A),

(b) 0-200 parts by weight per unit time of the fresh styrene monomer,and

(c) 0.01-0.9 parts by weight of the organic peroxide, and conductingpolymerization until the total polymerization yield of the styrenemonomer becomes at least 1.5 times more than that of the step (A) in thefinal stage (hereinafter referred to as the step (B)).

The total amount of an organic peroxide to be added as an initiator forradical polymerization in the step (A) of the present invention is setto be less than 0.01 parts by weight (include 0), and more preferably0.003 parts by weight, for 100 parts by weight of styrene monomersupplied to the 1st reactor in the step (A). If the amount exceeds 0.01parts by weight, effects of the present invention are not to beachieved. When the resin manufactured by adding an organic peroxide inan amount exceeding 0.01 parts by weight is electron-microscopicallyobserved, numerous rubber particles having a finer diameter than thoseof the resin manufactured according to the present invention method areobserved. Formation of such particles seems to hinder manifestation ofthe advantages of the present invention. To the 1st reactor of the step(A), a butadiene polymer is added in a range of 3 to 15 parts by weight,and more preferably in the range of 4-12 parts by weight, for 100 partsby weight of styrene monomer. According to the method of the presentinvention, formation of rubber dispersing particles occurs in the step(A) as is also well known in the art. Outside the range of 3-15 parts byweight, diameter modification of the dispersing particles becomesdifficult, the rubber particle diameters within the product resinfluctuate during the manufacturing operation, and it becomes difficultto obtain a product with a stable quality.

The reason why one or more agitator type polymerization reactorsconnected in series are used in the step (A) as the polymerizationreactor in the present invention method is to facilitate the abovementioned dispersing particle formation. The number of such agitatortype polymerization reactors may be one or more, and there is nospecific limitation placed on the said number. Polymerization of astyrene monomer in the step (A) is conducted in the final reactor of thestep (A) (the polymerization reactor in the step (A) if only onepolymerization reactor is used) until the total polymerization yield ofthe styrene monomer is in the range of 2.0 to 5.0 times more than theamount of a butadiene polymer supplied, or more preferably in the rangeof 2.3 to 3.5 times. If it is less than 2.0 times, or more than 5.0times, the advantages of the present invention are not manifested. Thepresent invention method provides the step (B) where organic peroxide issupplied to a polymerization solution in such a specific state tocontinue polymerization.

In the step (B) of the present invention, there are supplied the fullamount of the polymerization liquid discharged from the step (A) and0-200 parts by weight per unit time, or more preferably 0-150 parts byweight, of the fresh styrene monomer to the first reactor vessel of thestep (B). This supply of the styrene is useful in adjusting the rubbercontent in the product resin. When the supply exceeds 200 parts byweight, dispersion stability of rubber particles formed in the step (A)becomes deteriorated, and adjustment of rubber particle diameter becomesdifficult.

In the step (B) of the present invention method, 0.01-0.9 parts byweight per unit time of an organic peroxide for 100 parts by weight perunit time of the styrene monomer supplied to the 1st reactor in the step(A) must be supplied to the reactor in the 1st stage of the step (B). Weshall further explain the amount of the organic peroxide to be supplied.When the sum of the amount of the unreacted styrene monomer in thepolymerization liquid formed in the step (A) to be supplied to thereactor in the 1st stage of the step (B) per unit time and the amount ofthe styrene monomer to be freshly supplied per unit time to the reactorin the 1st stage of the step (B) is set at 100 parts by weight, then theamount of the organic peroxide to be supplied should be selected to bewithin the range of 0.009 to 0.31 parts by weight per unit time, or morepreferably in the range of 0.01 to 0.2 parts by weight. The figures aresignificant in that the effects of the present invention are notachieved with less than 0.009 parts by weight of the organic peroxide.This is presumably because a certain reaction product is formed by acertain amount of the organic peroxide supplied in the step (B), andsuch a reaction product works specifially on the butadiene polymerconverted to a specific state in the step (A), thereby bringing aboutthe effects of the present invention. If the addition amount exceeds0.31 parts by weight, Izod Impact value of the product resin becomeslowered, and there arises difficulties to its performance as an impactresistant resin. When the organic peroxide is to be supplied also in thestep (A), it does not matter whether the types of the organic peroxidesused in the steps (A) and (B) are the same or different. This range of0.009-0.31 parts by weight is so set in the present invention becausethe polymerization yield of the styrene monomer in the step (A) iscontrolled by the weight of rubber, and also because the polymerizationyield in the step (B) should be 1.5 times or more than that in the step(A), thus placing a limitation on the amount of the styrene monomer tobe supplied in the step (B). Therefore, the latter is limited to bewithin the range of 0.01-0.9 parts by weight for 100 parts by weight ofthe styrene monomer supplied in the step (A).

The polymerization yield of the styrene monomer in the step (B) shouldbe at least 1.5 times more than that of the step (A), or more preferablymore than 2 times. If it is less than 1.5 times, the advantages of thepresent invention are not achievable, presumably because the abovementioned organic peroxide does not become fully active. The organicperoxide is supplied to the steps (A) and (B) by dissolving in thestyrene monomer to be fed, or in the solution of ethylbenzene ortoluene, or by dispersing in a dispersing agent or fluidizing agent suchas paraffin.

The organic peroxide used in the present invention may be any which hasa function of initiating polymerization for a styrene monomer such asmethylethyl ketone peroxide,1.1-bis(t-butylperoxy)3.3.5-trimethylcyclohexane,1.1-bis(t-butylperoxy)cyclohexane, n-butyl-4.4-bis(t-butylperoxy)valerate, 2.2-bis(t-butylperoxy)butane, t-butyl hydroperoxide, cumenehydroperoxide, di-isopropyl benzene hydroperoxide, p-menthanehydroperoxide, 2.5-dimethylhexane 2.5-di-hydroperoxide,1.1.3.3-tetramethylbutyl hydroperoxide, di-t-butyl peroxide,t-butylcumyl peroxide, di-cumyl peroxide, , '-bis(t-butylperoxyisopropyl)benzene, 2.5-dimethyl-2.5-di(t-butyl peroxy)hexane,2.5-dimethyl-2.5-di(t-butyl peroxy) hexane-3, acetyl peroxide, t-butylperoxy acetate, t-butyl peroxy isobutylate, t-butyl peroxy 2-ethylhexanoate, t-butyl peroxy 3.5.5-trimethyl hexanoate, t-butyl peroxylaurate, t-butyl peroxy benzoate, di-t-butyl diperoxy isophthalate,2.5-dimethyl-2.5-di(benzoyl peroxy)hexane, t-butyl peroxy maleic acid,t-butyl peroxyisopropyl carbonate. One or more than two of the abovecompounds may be used.

At least one of monomers selected from styrene, alkyl styrenes such asmethyl styrene, ethylstyrene, isopropyl styrene, halogenated styrenesuch as chloro styrene, bromostyrene, or halogenated alkyl styrene isused as the styrene monomer in the present invention. In supplying thestyrene monomer, it may be substituted in part with a monomer which canbe radical-polymerized with styrene monomer. Examples of such monomersare acrylonitrile, methacrylonitrile, vinylidene cyanide, acrylic acidand alkyl esters of acrylic acid.

Examples of the butadiene polymer used in the present invention arepolybutadiene rubber manufactured by the emulsion polymerization method,and polybutadiene rubber manufactured by the solution polymerizationmethod using stereospecific catalyst or organic lithium catalyst. Whenusing such a polybutadiene polymer, a portion thereof may be substitutedby isoprene polymer or styrenebutadiene copolymer rubber.

In the method of the present invention, such solvents as ethylbenzene,ethyltoluene, toluene, xylene, ethylxylene, diethylbenzene may besupplied to the polymerization vessel. Although there is no specificlimit set on the amount of such a solvent, it is preferred that theamount should not exceed 50 parts by weight for 100 parts by weight oftotal styrene monomer supplied to the polymerization reactor. This isbecause the solution decreases the polymerization volume and becauserecovery of solution is rather labor consuming.

In the method of the present invention, it is necessary to polymerize astyrene monomer throughout the two steps of (A) and (B). The advantagesof the present invention are not achieved by step (A) or (B) alone. Thisis because of the fact that the present invention manifests itsadvantages by reacting an organic peroxide with a butadiene polymer in aspecific state.

There are no limitations to be placed on the type or the structure ofthe single or plural number of reactors connected in series and used inthe step (B) of the present invention. They may be agitator type reactor(reactor with agitator), or the column type reactor.

In the present invention method, fluidizing agent such as paraffin,various types of antioxidants, or molecular weight regulator such asmercaptan may be added to the polymerization reactors.

Rubber modified polystyrene resin obtained by the present invention maybe used singly, or in combination with other styrene resins depending onthe uses. The resin obtained by the present invention may be used incombination with stabilizers generally used with styrene resins againstthe heat, light, and oxygen, flame retarding agents, plasticizers,coloring agents, lubricants, and antistatic agents.

The present invention method remarkably improves the impact resistanceof the portions where polystyrene molecule orientation is likely tooccur in the molded product made from rubber modified styrene resinmanufactured in accordance with the present invention. This is not atall anticipated from the conventional arts, and its industrial utilityvalue is extremely valuable.

The examples of the present invention are now given:

EXAMPLE 1 a. Method of Manufacture

Polymerization was conducted using an agitator type polymerizationapparatus comprising serially connected three stage polymerizationreactors. To the polymerization reactor of the 1st step (Step (A) of thepresent invention) was continuously supplied 108 parts by weight perunit time of butadiene polymer solution made up by dissolving 8 parts byweights of butadiene polymer (Dien 55 available from Asahi ChemicalIndustry Co., Ltd.) in 100 parts by weight of styrene, and to thepolymerization reactor of the 2nd stage (Step (B) of the presentinvention) were continuously supplied 45 parts by weight of styrene, 20parts by weight of ethylbenzene, and 0.07 parts by weight of di-t-butylperoxide. The polymerization temperature for each of the polymerizationreactor in the stages 1 to 3 was set at 140° C., 130° C. and 133° C.respectively. Polymerization liquid from the polymerization reactor inthe 3rd stage was introduced to a volatile matter removing device toremove unreacted monomer and ethylbenzene. The device was operated at atemperature of 220° C. and at a degree of vacuum of 20 torr. Thepolymerization yield of styrene monomer in the polymerization reactor inthe 1st stage was 21%, while overall polymerization yield in the threestages was 81%.

Accordingly, the rubber content of the product resin was 6.4%. In thefollowing examples, the volatile matter removal was conducted under theidentical conditions as those of the present example.

b. Molding and Evaluation

Molding was conducted in the following manner. Using an injectionmolder, a dumb-bell test piece was molded at the molding temperature of210° C. The dimensions were; length 21.5 cm, thickness 0.32 cm, widths 2cm at both ends and 1.3 cm at the center. The gate portion for the molddies was the end portions and the diameter of the gate was 0.2 cm. Atthe same time, notched Izod test piece was also molded. Evaluation ofimpact strength by the falling weight test at the portions wherepolystyrene orientation tended to occur was conducted in the followingmanner.

In order to seek out the portions where polystyrene molecule orientationtends to occur in the said dumb-bell test piece, polystyrene resin withmolecular weight of 130,000 was molded under the same conditions asmentioned above as a standard product. The test piece taken from such aproduct was heated at 90° C. for 6.5 hours, and the contraction ratiosof various portions of the molded product were sought. At the end of thedumb-bell test piece which is not the gate portion, the contraction inthe direction of the length was 1% while it was 9% at the center. Thecontraction ratio at the center was extremely high suggesting that thecenter portion is where the polystyrene molecule orientation tended tooccur most. Thus, by evaluation of the impact strength by the fallingweight test at the center, the advantages of the present inventionbecome apparent. Measurement of the falling weight impact strength wasperformed by dropping vertically a metallic weight at the center of thedumb-bell test piece placed horizontally, and by gradually increasingthe height from which the weight is dropped, the height at which thetest piece cracks is sought, and the sum of thus obtained height and theweight of the metallic weight was used in evaluating the impactstrength. For evaluating the general impact strength of the resin Izodimpact value was measured in a method similar to that of ASTM-D-256. Theresults are shown in Table 1. Excellent effects of the present inventionare clearly observed.

EXAMPLE 2

A polymerization apparatus of a similar type as that of Example 1 wasused, and 100 parts by weight per unit time of styrene was supplied tothe 1st polymerization vessel while 10 parts by weight of butadienepolymer was supplied to the 1st polymerization vessel. To the 2ndpolymerization vessel were supplied per unit time 80 parts by weight ofstyrene, 30 parts by weight of ethylbenzene, and 0.2 parts by weight of2.5-dimethyl-2.5-di(t-butyl peroxy)hexane, and the polymerizationtemperature of the first to the third tanks was set at 135° C., 130° C.and 135° C. respectively. The polymerization yield of styrene monomer inthe 1st stage was 29%, while overall polymerization yield in the threestages was 84%. The rubber content of the product resin was 6.2%. Theimpact strength was measured similarly as in Example 1. Table 1 showsthe results thereof.

EXAMPLE 3

A polymerization apparatus of a similar type as that of example 1 wasused, and for 100 parts by weight per unit time of styrene supplied tothe 1st polymerization vessel, 5 parts by weight of butadiene polymerwas supplied to the 1st polymerization vessel, 20 parts by weight ofstyrene, 10 parts by weight of ethylbenzene, and 0.03 parts by weight of2.5-dimethyl-2.5-di(benzoyl peroxy)hexane were supplied to the 2ndpolymerization vessel. The polymerization temperature of the 1st to the3rd vessels was set at 132° C., 135° C., and 135° C. respectively. Thepolymerization yield of styrene in the vessel in the 1st stage was 19%while overall polymerization yield in three stages was 60%. The rubbercontent of the product resin was 6.0%. The impact strength was measuredsimilarly as in Example 1. Table 1 shows the results thereof.

EXAMPLE 4

Polymerization was conducted using an agitator type polymerizationapparatus comprising a continuous series of 4 stage polymerizationvessels. To the polymerization vessel in the 1st stage were continuouslysupplied 100 parts by weight per unit time of styrene, 7 parts by weightof butadiene polymer, and 0.003 parts by weight of2.5-dimethyl-2.5-di(t-butyl peroxy)hexane. To the polymerization vesselof the third stage were supplied 10 parts by weight per unit time ofstyrene, 13 parts by weight of ethylbenzene, and 0.05 parts by weight of2.5-dimethyl-2.5-di(t-butyl peroxy)hexane. The polymerizationtemperature of the 1st to the 4th polymerization vessels was set at 132°C., 132° C., 134° C. and 140° C. respectively. The polymerization yieldof styrene monomer in the polymerization vessel in the 2nd stage was16%, while overall polymerization yield was 93%. The rubber content inthe product resin was 6.4%. The evaluation similar to Example 1 wasperformed and the results are shown in Table 1.

EXAMPLE 5

Polymerization was conducted in a polymerization apparatus comprisingtwo stage agitator type reaction vessels and a column reactor in the 3rdstage connected in series. To the reaction vessel in the 1st stage wascontinuously supplied 107 parts by weight per unit time of butadienepolymer solution in which 7 parts by weight of butadiene polymer for 100parts by weight of styrene was dissolved. To the column reactor in the3rd stage were supplied 20 parts by weight of per unit time of styrene,20 parts by weight of ethylbenzene, and 0.05 parts by weight of2.5-dimethyl-2.5-di(benzoyl peroxy)hexane. The temperature of the 1stand the 2nd polymerization vessels was set at 136° C., and thepolymerization temperature at the outlet of the third polymerizationvessel at 160° C. The polymerization yield of styrene monomer at the 2ndreactor was 25% while overall polymerization yield in three stages was90%. The rubber content in the product resin was 6.1%. The impactstrength was measured similarly as in Example 1 and the results areshown in Table 1.

COMPARATIVE EXAMPLE 1

A polymerization apparatus of the similar construction as that ofExample 1 was used, and the conditions identical to those of Example 1were followed for supplying the starting material to the apparatusexcept that organic peroxide was not supplied to the 2nd polymerizationvessel. The reaction temperature of the 1st to the 3rd polymerizationvessels was set at 140° C., 142° C. and 142° C. respectively. Thepolymerization yield of styrene in the 1st polymerization vessel was 19%while overall polymerization yield in three stages was 78%. Accordingly,the rubber content in the product resin was 6.6%. The impact strengthdetermined similarly to Example 1 is shown in Table 1.

COMPARATIVE EXAMPLE 2

A polymerization apparatus of the similar construction as of Example 1was used, and the conditions identical to those of Example 2 werefollowed for supplying the starting material except that2.5-dimethyl-2.5-di(t-butyl peroxide)hexane was not supplied to the 2ndpolymerization tank, and 0.15 parts by weight of the same substance wassupplied to the 1st polymerization vessel. The reaction temperature atthe 1st to 3rd polymerization vessels was set at 130° C., 136° C. and137° C. respectively. The polymerization yield of styrene in the 1ststage was 24%, while overall polymerization yield in three stages was81%. Accordingly, the rubber content of the product resin was 6.4%.

The impact strength was measured in a manner similar to that of Example1, and the results are shown in Table 1.

COMPARATIVE EXAMPLE 3

The polymerization apparatus with an identical construction as that ofExample 1 was used, and the raw materials were supplied under theconditions identical to those of Example 3. The polymerizationtemperature of the 1st to the 3rd polymerization vessels was set at 138°C., 130° C. and 130° C. respectively. The polymerization yield ofstyrene in the 1st polymerization vessel was 29% while overallpolymerization yield in three stages was 60%. The rubber content in theproduct resin was 6.5%. The impact strength was measured similarly as inExample 1 and the results are shown in Table 1.

COMPARATIVE EXAMPLE 4

A polymerization vessel of the similar construction as Example 1 wasused, and the polymer starting materials were supplied under theconditions identical to those of Example 1 except that the amount ofdi(t-butyl peroxide) supplied to the 2nd polymerization vessel waschanged to 1.0 parts by weight per unit time for 100 parts by weight ofstyrene supplied per unit time to the polymerization vessel in the 1ststage. The reaction temperature at the 1st to the 3rd polymerizationvessels was set at 140° C., 130° C. and 125° C. respectively. Thepolymerization yield of styrene in the 1st polymerization vessel was 21%while overall polymerization yield in three stages was 78%. The rubbercontent of the product resin was 6.6%. The impact strength was measuredin a manner similar to that of Example 1, and the results are shown inTable 1.

                                      TABLE 1                                     __________________________________________________________________________    Impact Strength Evaluated by Falling Weight Test                              of Rubber Modified Styrene Resin where Orientation                            of Styrene Resin is Likely to Occur                                                  Organic Peroxide                                                                       Polymerization                                                                        Polymerization           Impact Strength                     Addition *1                                                                            Yield in                                                                              Yield in        Izod Test Impact                                                                       Evaluated by                        (parts by weight)                                                                      Step A *2                                                                             Step B *3                                                                             Rubber Content                                                                        Strength Falling Weight                      Step A                                                                             Step B                                                                            (Times) (Times) (%)     kg · cm/cm                                                                    kg · cm             __________________________________________________________________________    Example 1                                                                            --   0.07                                                                              2.63    4.59    6.4     8.9      19.5                         Example 2                                                                            --   0.2 2.90    4.21    6.2     9.5      21.4                         Example 3                                                                            --   0.03                                                                              3.80    2.79    6.5     9.2      20.3                         Example 4                                                                            0.003                                                                              0.05                                                                              2.29    5.39    6.4     9.4      18.5                         Example 5                                                                            --   0.05                                                                              3.57    3.32    6.1     9.1      24.0                         Comparative                                                                   Example 1                                                                            --   --  2.38    4.95    6.6     8.9      11.0                         Comparative                                                                   Example 2                                                                            0.15 --  2.40    5.08    6.4     9.4      9.8                          Comparative                                                                   Example 3                                                                            --   0.03                                                                              5.80    1.48    6.5     9.0      9.6                          Comparative                                                                   Example 4                                                                            --   1.0 2.63    4.38    6.6     5.2      4.5                          __________________________________________________________________________     *1 Amount of styrene momomer supplied to the 1st vessel of Step A is set      as 100 parts by weight.                                                       ##STR1##                                                                      ##STR2##                                                                 

We claim:
 1. In a method of continuously manufacturing rubber modifiedstyrene resins from a styrene monomer and a butadiene polymer by bulkpolymerization or solution polymerization using an organic peroxide asan initiator of radical polymerization, the improvement comprising:(A) afirst step of using a single or a plural number of agitator typepolymerization vessels connected in series, continuously supplying 100parts by weight of the styrene monomer and 3 to 15 parts by weight ofthe butadiene polymer per unit time to the first polymerization vessel,feeding continuously 0 to 0.003 parts by weight of the organic peroxideper said unit of time to the first vessel in full amount or to aplurality of polymerization vessels in divided portions, and conductingpolymerization until the polymerization yield of the styrene monomer inthe final polymerization vessel becomes 2 to 5 times more than theweight of the butadiene polymer; and (B) a second step of continuouslyfeeding to the first stage of a single or plural number of reactorsconnected in series the full amount of polymerization liquid dischargedfrom the first step, 0 to 200 parts by weight of fresh styrene monomerper said unit of time, and 0.01 to 0.2 parts by weight of fresh organicperoxide per said unit of time, and conducting polymerization until thepolymerization yield of the styrene monomer in the final stage is atleast 1.5 times the yield in the first step.
 2. A method as claimed inclaim 1 wherein the polymerization yield of the styrene monomer in thefinal polymerization stage in said first step is 2.3 to 3.5 times morethan the weight of the butadiene polymer.
 3. A method as claimed inclaim 1 wherein the amount of styrene monomer freshly fed in the secondstep is 0 to 150 parts by weight.
 4. A method as claimed in claim 1wherein the polymerization yield of the styrene monomer in the finalstage of said second step is more 2 times than the yield in said firststep.
 5. A method as claimed in claim 1 wherein the reactor used in thesecond step is a column type reactor.
 6. A method as claimed in claim 1wherein said styrene monomer is styrene, an alkyl styrene, a halogenatedstyrene or a halogenated alkyl styrene.
 7. A method as claimed in claim6 wherein said styrene monomer is in part substituted with a monomerradical-copolymerizable with said styrene monomer.
 8. A method asclaimed in claim 7 wherein said monomer radical-copolymerizable with thestyrene monomer is acrylonitrile, methacrylonitrile, vinylidene cyanide,or an alkyl ester of acrylic acid or methacrylic acid.
 9. A method asclaimed in claim 1 wherein said butadiene polymer is a polybutadienerubber prepared by an emulsion polymerization process or a solutionpolymerization process using a stereospecific catalyst or an organiclithium catalyst.
 10. A method as claimed in claim 9 wherein saidbutadiene polymer is substituted in part by isoprene polymer orstyrene-butadiene copolymer rubber.